feat: initial metric client implementation

[jvanschie]

Change Description

Introduced mgo-metric-service, a Python metrics client library that decouples application code from metrics backends. Applications emit counters, gauges, and timings through a single MetricsClient API, with pluggable backends (StatsD, in-memory, no-op) and formatters for metric keys and tags.

Changes Made

• Added MetricsClient with incr, gauge, and timing methods, optional tag support, and debug logging
• Implemented backends: StatsDBackend (StatsD over UDP), InMemoryBackend (records calls for inspection), and NoopBackend (discards metrics)
• Implemented formatters: StatsDFormatter (dot-separated keys with tag validation), InMemoryFormatter (human-readable keys for tests), and NoopFormatter formatting nothing.
• Added FakeMetricsClient with assert_metric_call, assert_incr, assert_gauge, assert_timing, and reset for test assertions
• Updated CI workflow to run make check (lint, format, mypy, pytest with coverage)
• Updated README.md with installation, usage examples, and testing guidance

Testing Instructions for QA Team

This is a Python library, not a deployable HTTP service.
Verification is through automated checks or library usage.

Checklist

• The pull request is linked to the corresponding GitHub issue.
• The developer confirms that this pull request has been verified against the Pull Request Checklist.
• I've read the contributing document
• I've read and understand the Code of Conduct
• I've signed off all commits in this pull request in accordance with the Developer Certificate of Origin (DCO)

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud